A bumper beam in which strength in the lengthwise direction is made uniform is known as a bumper beam structure for a vehicle, as disclosed in Japanese Patent Application Laid-Open Publication No. 2001-26245 (JP 2001-026245 A).
The bumper beam disclosed in JP 2001-26245 A will be discussed below with reference to FIGS. 12 and 13 hereof.
A reinforcement structure 100 as a bumper beam mounted on a vehicle bumper comprises a back wall 101 provided perpendicular to a loading direction X1; an upper rib 102 and a lower rib 103 that extend from an upper end and a lower end, respectively, of the back wall 101 in an opposite direction from the loading direction X1; a middle rib 104 that extends from the center of the upper and lower ends of the back wall 101 in an opposite direction from the loading direction X1; an upper portion 106 of the front wall that extends downward from the distal end of the upper rib 102; a lower portion 107 of the front wall that extends upward from the distal end of the lower rib 103; and a triangular bead 108 formed by connecting the upper portion 106 of the front wall and the middle rib 104 to each other, and connecting the lower portion 107 of the front wall and the middle rib 104 to each other, as seen in FIG. 12. The upper portion 106 of the front wall and the lower portion 107 of the front wall constitute the front wall 109.
FIG. 13 shows the bumper apparatus for housing the bumper beam shown in FIG. 12.
The bumper apparatus 110 of a vehicle comprises a reinforcement structure 100 mounted on a vehicle body 111, a cushioning material 112 disposed in front of the reinforcement structure 100, and an outer casing 113 that covers the reinforcement structure 100 and the cushioning material 112, as seen in FIG. 13.
The reinforcement structure 100 described above is uniformly strong in the lengthwise direction (the front-to-back direction of the drawing surface). Therefore, when the bumper apparatus 110 provided to, e.g., the front end of a subject vehicle has collided with a bumper apparatus of another vehicle, a wall, or other object having a relatively large surface area, a large collision reaction force is generated by receiving the collision load over the entire bumper apparatus 110 of the subject vehicle, and the collision energy is absorbed. However, when the bumper apparatus 110 of the subject vehicle collides with, e.g., the center pillar of a side surface of another vehicle, the collision load is concentrated on the center pillar, and the center pillar greatly deforms because the collision surface area between the bumper apparatus 110 and the center pillar is small.
A preferred bumper beam structure is one that reduces the collision reaction force generated by the bumper beam and suppresses deformation of the collision part even when the surface area of the collision part is small, and generates a sufficient collision reaction force when the surface area of the collision part is large.